Automatic transmission fluid of reduced susceptibility oxidative degradation



United States Patent AUTOMATIC TRANSMISSION FLUID OF REDUCED SUSCEPTIBILITY OXIDATIVE DEGRADATION Maurice K. Rausch, Homewood, Ill., assignor to Sinclair Research, Inc., New York, N.Y.

No Drawing. Continuation-impart of application Ser. No. 436,643, Mar. 2, 1965. This application Aug. 22, 1967, Ser. No. 662,302

Int. Cl. Cm 1/44 US. Cl. 25275 6 Claims ABSTRACT OF THE DISCLOSURE A lubricating composition containing; a major amount (e.g. about 51 to 80% by volume) of a solvent-refined distillate mineral oil having a viscosity index of about 90 to 100, a pour point of about 10 to F., and a viscosity of about 10 to 43 cs. at 100 F.; a petroleum naphthenic lubricating oil having an API gravity of 24 to 30, a flash of 240 to 320 F., a viscosity of 6 to 20 cs. at 100 F., a viscosity index of 20 to '80, a pour point of 80 to -40 F., a specific dispersion (n of 98 to 104 and an aromatic content of up to about 3%; and an antioxidant which can be either an oil-soluble metal salt of a diester dithiophosphoric acid (e.g. zinc di(methyl amyl) dithiophosphate) or an oil-soluble alkaline earth metal thiophenate (e.g. barium thiophenate). The naphthenic oil is present in an amount of about 20 to 49% by volume of the total volume of the distillate mineral oil and naphthenic oil components, the antioxidant being employed in an amount of about 0.2 to 5 wt. percent based on the total weight of the distillate mineral oil and naphthenic oil components.

This application is a continuation-in-part of application Ser. No. 436,643, filed Mar. 2, 1965, now abandoned.

The present invention is directed to automotive automatic transmission fluids possessing superior performance characteristics especially as to transmision cleanliness and fluid life as measured by resistance to oxidative deterioration.

In automatic transmissions employing fluid drive or torque converters, a hydraulic fluid performs the functions of a power transmission medium, a heat transfer medium and a lubricant for bearing surfaces. Rigorous requirements have been set up to qualify fluids for use in automotive automatic transmissions. These requirements include a viscosity index (ASTM) of at least 130, a flash point of about 330 F. minimum, a pour point of below about F., and in addition the fluid must pass the copper strip'corrosion test and must possess good oxidative resistance.

In order to meet the requirements mentioned above it has been necessary to utilize particular lubricating oil bases together with certain additives in formulating satisfactory automatic transmission lubricants. Suitable base oils and additives are known to the art and the additives are often made commercially available as an additive package for use in automatic transmission base fluids.

I have now found an automatic transmission fluid base oil blend, which, after the addition of certain antioxidants and other additives to the blend provides a final base transmission fluid meeting the aforementioned requirements and having markedly reduced susceptability to oxidative deterioration. The base oil blend employed in the invention is a blend of two different mineral lubricating oils to which has been added an antioxidant which can be either an oil-soluble metal salt of a diester dithiophosphoric acid or an oil-soluble alkaline earth metal thiophenate. One of the oils of the blend is a solvent-refined 3,450,636 Patented June 17, 1969 "ice neutral or distillate oil commonly employed as the base oil in automatic transmission fluids. The solvent-refined neutral oil is characterized by having an viscosity index (ASTM) of about 90 to 100, a viscosity, at 10 F. of about 10 to 43 centistokes, and a pour point of about -10 to +20 F. The neutral oil constitutes the major portion of the base oil blend of the invention, usually being present in an amount of about 51 to by volume.

The second essential oil of the base fluid blend of the invention is a naphthenic mineral lubricating oil having the following approximate characteristics:

Pour, F 80 40 Specific dispersion, n 98-104 Various petroleum and other mineral naphthenic lubricating oils having these physical characteristics can be used as the minor oil component of the base oil blend of the invention and various methods of the art for obtaining naphthenic lubricating oil with these characteristics can be utilized in making this component. The naphthenic base oil component will generally constitute about 20 to 49% by volume of the base oil blend.

A preferred method of obtaining the naphthenic base oil component comprises subjecting a petroleum naphthenic fraction derived from a naphthenic base crude such as a gulf coast or California crude to a dual hydrogenation process. If the crude oils contain a wax, they are preferable dewaxed prior to the first hydrogenation although the dewaxing can follow the first hydrogenation. This dewaxing can be carried out for example by a solvent treatment using methyl ethyl ketone and toluene as the solvent to produce an oil of below 25 F. pour point (ASTM D-97).

The dual hydrogenation comprises first contacting the naphthenic base feed portion in the presence of hydrogen with a sulfur-resistant hydrogenation catalyst. Such catalysts usually have as an active component a so-called hydrogenation metal, for instance, selected from the group consisting of tin, vanadium, metals of Groups V-B and VIB in the Periodic Table, e.g. vanadium, niobium, molybdenum and tungsten, and metals of the iron group. This hydro-treating is conducted at a temperature of about 400 to 800 F., preferably about 600 to 750 F. The other reaction conditions generally include pressures of about 300 to 5000 p.s.i.g., preferably about 1000 to 3000 p.s.i.g.; weight hourly space velocities (WHSV) of about 0.1 to 5, preferable about 0.2 to 2; and molecular hydrogen to oil ratios of about 500 to 2500 standard cubic feet of hydro gen per barrel of oil.

The hydrogenated oil from the first hydrogenation stage is then subjected to a second hydrogenation operation which involves contacting the hydrogenated oil in the presence of hydrogen with a platinum group metal-promoted hydrogenation catalyst at a temperature of about 400 to 800 F., preferably about 500 to 750 F. The other reaction conditions generally include pressures of about 300 to 5000 p.s.i.g., preferably about 1000 to 3000 p.s.i.g., space velocities (WHSV) of about 0.1 to 5, preferably about 0.2 to 1; and molecular hydrogen to oil ratios of about 1000 to 10,000 standard cubic feet of hydrogen perbarrel of oil, preferably about 2000 to 5000 standard cubic feet of hydrogen per barrel of oil.

The catalyst of the first hydrogenation operation can be the sulfur-resistant catalysts conventionally employed in the hydrogenation of heavy petroleum oils. Examples of suitable catalytic ingredients are tin, vanadium, members of Group VIB in the Periodic Table, i.e. chromium, molybdenum and tungsten, and metals of the iron group,

i.e. iron, cobalt and nickel. Generally, these meals are present in catalytically effective amounts for instance about 2 to 30 or more weight percent, and are usually present in the form of oxides and sulfides. Mixtures of these materials or compounds of two or more of the oxides or sulfides can be employed, for example, mixtures or compounds of the iron group, metal oxides or sulfides with the oxides or sulfides of Group VIB constitute very satisfactory catalysts, Examples of such mixtures or compounds are nickel molybdate, tungstate or chromate (or thiomolybdate, thio-tungstate or thiochromate) or mixtures of nickel or cobalt oxides with molybdenum, tungsten or chromium oxides. As the art is aware, these catalytic ingredients are generally employed while disposed upon a suitable carrier of the solid oxide refractory type, e.g. a predominantly calcined or activated alumina. Commonly employed catalysts have about 1 to 10% of an iron group metal annd to 25% of a Group VIB metal (calculated as the oxide). Advantageously, the catalyst is cobalt molybdate or nickel molybdate supported on alumina. Such preferred catalysts can be prepared by the method described in US. Patent 2,938,002 issued May 24, 1960 to Carl D. Keith et al.

As aforementioned, the catalyst of the second hydrogenation operation of the present invention is a platinum group metal-promoted catalyst. This catalyst is to be distinguished from the catalysts of the first hydrogenation in that it is not normally sulfur-resistant. The catalyst includes catalytically effective amounts of the platinum group metals of Group VIII, for instance platinum palladium, rhodium or iridium. The catalytic amount of metal on a suitable carrier such as alumina usually falls within the range of about 0.01 to 2 weight percent, preferably about 0.1 to 1 weight percent. The small amount of platinum group metal may be present in the metallic form or as a sulfide, oxide or other combined form. The metal may interact with other constituents of the catalyst but if during use the platinum group metal be present in metallic form, then it is preferred that it be so finely divided that it is not detectable by X-ray diffraction means, i.e. that it exists as crystallites of less than 50 A. size. Of the platinum group metals, platinum is preferred. If desired, the catalysts of the first and second hydrogenations can be prereduced prior to use by heating in the presence of hydrogen, generally at temperatures of about 500 to 900 F.

Although any of the solid refractory type carriers known in the art may be utilized as a support for the platinum group metal the preferred support is composed predominantly of alumina of the activated or calcined type. The alumina base is usually the major component of the catalyst, generally constituting at least about 75 weight percent of the basis ofthe catalyst and preferably at least about 85 to 99.8 percent. This catalyst base is an activated or gamma-alumina such as those derived by calcination of amorphous hydrous alumina, alumina monohydrate, alumina trihydrate or their mixtures. The catalyst base precursor most advantageously is a mixture containing a major proportion, for instance about 65 to 95 weight percent of one or more of the alumina trihydrates bayerite I, nordstrandite (randomite) or gibbsite, and about 5 to 35 weight percent of alumina monohydrate (boehmite), amorphous hydrous alumina or their mixture. The alumina base can contain small amounts of other solid oxides such as silica, magnesia, natural or activated clays (such as kaolinite, montmorillonite, halloysite, etc.), titania, zirconia, etc., or other mixtures.

Following either of the hydrogenation operations of the present invention the hydrogenated oils in each case may be distilled or topped if desired to remove any hydrocracked or other light materials that may have been formed and to increase the flash point of the oil. Whether or not topping is desired may depend on the particular lubricating oil fraction being hydrogenated and the particular hydrogenation conditions employed. Thus, the amount of topped overhead that may be taken off in the .4 topping or distillation step after the first hydrogenation operation may often vary from about 0 to 50%, with about 0 to 25 being preferred. Likewise, the amount of overhead taken off in the topping or distillation operation after the second hydrogenation usually varies from about 0 to 50% with about 0 to 25% being preferred.

The dual hydrogenation operations of the present invention are thus conducted to reduce the aromatic carbon content of the initial naphthenic lubricating oil feed to 3% or below. As noted previously the initial naphthenic feed generally contains about 10 to 25% aromatics, less than about 65%, preferably less than about 50%, of paraffins with the essential balance being naphthenes. The viscosity of the naphthenic feed is generally about 50 to 2000, preferably 50 to 1200 SUS at F. The first hydrogenation usually accomplishes about 40 to 70% of the aromatic reduction and the second hydrogenation about 30 to 60% of the reduction.

Effective anti-oxidant and anti-corrosive additives in the base oil blend are the oil-soluble polyvalent metal salts derived from a wide variety of diester dithiophosphoric acids conventionally prepared by reacting a sulfide of phosphorous such as phosphorous pentasulfide, with an alcohol, phenol or mercaptan. These salts have the structure:

R-O/ \SM-- O-R The R groups in the acid esters may be aryl, e.g. phenyl, alkyl, aralkyl, cycloalkyl or other monovalent hydrocarbon groups which contain from about 3 to 20 carbon atoms, preferably about 3 to 12 carbon atoms, and may be further substituted in the organic portion. Of the polyvalent metals designated M in the above structure, zinc is preferred but other metals of 28 to 30 atomic number, i.e. nickel and copper, are suitable. Alcohols which may be employed in preparing the acid esters include primary and secondary alcohols such as 2-methyl amyl alcohol, 4- methylpentanol-Z,Z-methylpentanol-1, 2-ethylhexanol, diisopropyl carbinol, cyclohexanol, butanol-l, isopropanol and octadecanol-l or mixtures of high and low molecular weight alcohols. The preferred compounds are the zinc dialkyl dithiophosphates wherein the alkyl group contains about 3 to 12 carbon atoms, preferably about 3 to 8 carbon atoms. More specifically, the preferred compounds of this group include, for instance, dihexyl dithiophosphate, diheptyl dithiophosphate, di-2-methylamyl dithiophosphate, di-2-ethylhexyl dithiophosphate and the like. The antioxidants are usually employed in amounts of about 0.2 to 5% by weight, of the base oil.

Also effective in inhibiting oxidation and corrosion in the blends of the invention are oil-soluble alkaline earth metal thiophenates having the structural formula:

01) wherein M is an alkaline earth metal, R is a monovalent hydrocarbon group containing from about 3 to 20, preferably about 3 to 12 carbon atoms, and n is an integer of 0 to 3. Of the alkaline earth metals, calcium is preferred, but other divalent metals belonging to Group II of the Periodic Table such as berylium, barium, strontium and magnesium may be used. As in the case of the metal diester dithiophosphates discussed above, the monovalent hydrocarbon group R may be aryl, e.g., phenyl, alkyl, aralkyl, cycloalkyl, etc., and may be further substituted in the organic portion. Preferably, R is an alkyl group of 3 to 12 carbon atoms such as n-propyl, isopropyl, butyl, amyl, hexyl, cyclohexyl, octyl, nonyl, decyl, undecyl, dodecyl, etc. Some examples of the preferred alkaline earth metal thiophenates useful as antioxidants in the compositions of the invention are the calcium salts of amyl thiophenate, cyclohexyl thiophenate, 2,4-dioctyl thiophenate, 2,4-ethylhexyl thiophenate, etc.

In addition to the antioxidants discussed above, to the base oil blend can be added any of the conventional additives provided in automatic transmission fluids as, for instance, viscosity index improvers, detergents, corrosion inhibitors, anti-foam agents, etc.

Among the viscosity index improvers that can be employed, for example, are polymers such as the methacrylate polymers, polymers of olefins of 3 to 5 carbon atoms, polyvinyl ethers, fumarate-vinyl acetate copolymers, polyalkyl-styrenes, etc. and mixtures thereof.

The methacrylate polymers that can be used in our fluids include acrylic ester polymers usually having a molecular weight of about 5000 to 20,000. The series of commercially available polymers known as the Acryloids are particularly useful. Their chemical structure may be represented as:

1'1 (LO-R where R is a fatty alcohol radical of 6 to 18 carbon atoms such as cetyl, lauryl or octyl and n is the number of molecules of similar structure condensed together to form a high molecular weight polymer. The Acryloids are clear viscous concentrates of methacrylic polymer in a hydrocarbon solvent and the usual concentration of polymer is about 40 weight percent. Acryloid 710 is particularly useful. Acryloid 710, described in U.S. Patent No. 2,710,842, is a methacrylate polymer wherein R in the above formula is predominantly a mixture of lauryl and octyl groups and the molecular weight is about 10,000 to 20,000. Another commercial material of this type is Acryloid 150, wherein R is predominantly a mixture of cetyl, lauryl and octyl groups and the molecular weight of the polymer is about 10,000 to 15,000. Generally, the VI improvers are employed in amounts of about 1 to by weight of the base oil, preferably 1 to 3%.

Among the detergents, very popular ones are the basic aromatic sulfonates and basic phenates. The basic sulfonates can be prepared by neutralizing aromatic sulfonic acids with a theoretical excess of the hydroxides, chlorodies, oxides or other inorganic compounds of the alkaline earth metals so as to obtain a product which contains an amount of alkaline earth metal in excess of that theoretically required to replace the acidic hydrogens of the sulfonic acids. The preferred alkaline earth metal is barium. Generally preferred aromatic sulfonic acids are the oil-soluble mahogany sulfonic acids which can be derived from the treatment of a suitable petroleum oil, such as a liquid petroleum distillate boiling in the range of about 600 to 1000" F., with fuming sulfuric acid or sulfur trioxide, separating the resulting acid sludge from the acid treated oil and recovering the mahogany acids contained in the acid treated oil, The useful mahogany acids generally have a molecular weight of from about 300 to 500 or more, and although their exact chemical structures may vary, it appears that such acids are composed to a large extent of sulfonated aromatic hydrocarbons having either one or two aromatic rings per molecule, possible with one or more long chain alkyl groups containing from about 8 to 30 carbons atoms attached to the ring nuclei. The detergent additives when employed are generally incorporated in amounts of about 0.3 to 10% by Weight of the base oil.

Often it is customary in the automatic transmission package to include an anti-foam agent since the fluid is circulated rapidly in operation and air may be trapped in the oil. A suitable anti-foam agent is a silicone polymer of high viscosity, such as dimethyl silicone polymer having a kinematic viscosity at 25 C. of about 1000 centistokes and above, is advantageously employed. A silicone polymer is conveniently employed in the form of a concentrate in a hydrocarbon solvent, such as kerosene. For example, a very satisfactory anti-foam agent for this purpose is prepared by diluting 10 grams of a dimethyl silicone polymer (1000 cs. at 25 C.) with kerosene to bring the volume to 100 cc. A proportion of the order of about 0.0001 to .02 part by weight to this concentrate is ordinarily employed.

The following example is included to further illustrate the present invention.

EXAMPLE I A raw naphthenic base lube distillate obtained as a sidestream from the distillation of a gulf coast naphthenic base crude was hydrogen treated using a nickel-molybdena on alumina catalyst at process conditions of 1500 p.s.i.g., 700 F., 0.50 weight hourly space velocity, and 1500 s.c.f./ b. of feed hydrogen rate. The reactoreflluent from the hydrogenation was passed through a flash drum to remove a major portion of the gas and then through a stripper to remove the remainder of the gases and low boiling hydrocarbons.

The stripper bottoms or intermediate product was then put through a second hydrogenation step using a platinum on alumina catalyst at process conditions of 1500 p.s.i.g.,' 550 F., 0.25 WHSV and 5000 s.c.f./b. hydrogen rate. The reactor efiluent from this hydrogenation step was also passed through a flash drum and stripper to provide a stripper product designated Oil A. Pertinent tests on the feedstock, intermediate the final product are presented in Table I. 7

TABLE I Inter- Final mediate product; Feedstock product Oil Gravity, API 24. 1 27. 3 28. 4 Flash, F 270 275 285 Viscosity, cs. at 100 F 8. 30 8.093 8. 853 Viscosity index 33 52 54 Pour, F -65 60 Specific dispersion, no 133. 5 107. 4 98.5

Oil B Gravity, API 24.9 Flash, F. a 265 Viscosity, .cs. at 100 F. 9.396 Viscosity index 33 Pour, F. -65 Specific dispersion 125.1

Each of the base oil blends was formulated with the same additive package, specifically 7.7% of a commercial anti-oxidant detergent mixture which contains as tha antioxidant componentbarium thiophenate and which analyzes as follows: Physical tests;

Gravity, API 15.1 Flash, F, 395 Viscosity at 210 F. 133.4 Chemical tests, percent by weight a S Y 1.98 Ba 5.33' P 0.475 CO (release upon heating) 0.83 Base No. pH 4 22.3

6.5% polyisobutylene viscosity index improver and 0.0075% red dye color (all weight percents) to give formulated automatic transmission Fluids A and B. Characteristics of these fluids are listed in Table II.

The results of the transmission tests are shown in Table V below:

TABLE II TABLE V Fluid A Fluid B Composition Fluid C Fluid D (containing (containing 5 Oil A) Oil B) Base oil, vol. percent 30 2 35 Neutral oil 70 65 Gravity, 30.6 28. 9 Additives, wt. percent: Flash, 350 340 Antioxidant detergent 4. 9 4. Viscosity, cp VI improver 3. 3. 5 1 F 2, 470 3, 510 Red dye color 0. 0075 0. 0075 Viscosity, 08. at 110 F 40. 33 44. 49 Hours to initia1dep0s1ts 346 976 Viscosity index 148 143 Average i 9. 9 Pour -55 Average sludge 9. 8 J- These fluids were run in a full transmission test, specifi- Used 346 hrs 6001, 976 hm cally the L-39 Power-glide oxidation test with air bleed 0. 2 4. 287 at 275- F. sump temperature. Results of this testing were 8 3; 4,201 as follows: Acid No 4. as 4.24 6. 09

TABLE III Oil B. n 'dA r1 (1 B 2 on U1 ill The results demonstrate the superior performance of Hours to initial deposits 657 272 ivmge l g 3,; Fluid D, the com osition of the present 1nven 1onverage s u ge 9. 159%0118385'25; I bl 4 06 4 n EXAMPLES HI .$;Z, i.{fi.".. 3 The following automatic transmission fluid formula- Acid tion, when tested in the full transmission test of Examples '1 These results show the outstanding performance of Fluid A which ran 2.4 times as long as the control test. Despite the considerably longer running time, Fluid A exhibited equivalent oil deterioration and superior transmission cleanliness compared to the control test.

EXAMPLE 11 Oil B-of Example I blended with 70% of the neutral oil of Example I was compared with an oil blend of by volume Oil A of Example I and 65% by volume of the same neutral oil, using the L-39 Power-glide oxidation test with air bleed. Each of the base oil blends was formulated With additive packages of a polyisobutylene viscosity improver, red dye color and a commercial antioxidant-detergent mixture which contains as the anti-oxidant component zinc di(methyl amyl) dit-hiophosphate and which analyzes as follows:

Physical tests:

Gravity, API

The amounts of the additives employed are shown in Table V below. Characteristics of these fluids, designated Fluids C and D, are listed in Table IV:

TABLE VI Fluid 0 Fluid D (containing (containing Oil B) Oil A) Gravity, API 29. 0 Flash "F 340 Fire, F. 395 Brookfield vis.:

40 cp 10 cp... KV 100 F cs KV 210 F cs.-. VI P Percent P Percent Zn I and II also gives outstanding performance:

Additives: Wt. percent Basic barium sulfonate 1 4.7 Zinc di(methyl amyl) dithiophosphate 2 3.0 Sulfurized sperm oil 3 2.5 Slack wax 4 0.5 Methacrylate copolymer 5 3.7 Dimethyl silicone 0.002 Base oil:

% Mid-Continent neutral oil of Example I 30% Oil A of Example I following approximate characteristics:

Viscosity index About to Pour point, F. About 10to +20 Viscosity, cs. at 100 F. About 10 to 43 (B) about 20 to 49% by volume, based on the total volume of the A and B components, of a petroleum naphthenic lubricating oil having the following approximate characteristics:

Gravity, API 24-30 Flash, F. 240-320 Viscosity, cs. at 100 F 6-20 Viscosity index 20-80 Pour point, F. 80- 40 Specific dispersion, n 98-104 said naphthenic oil having an aromatic content of up to about 3%, and (C) about 0.2 to 5 wt. percent based on the total weight of the (A) and (B) components, of an antioxidant selected from the group consisting of an oil-soluble metal salt of a diester dithiophosphoric acid having the structure:

wherein M is zinc, nickel or copper and R is hydrocarbon of about 3 to 20 carbon atoms, and an alkaline earth metal thiophenate having the structure:

wherein X is an alkaline earth metal and R is hydrocarbon of about 3 to 20 carbon atoms and n is an integer of to 3.

2. The automatic transmission fluid of claim R is alkyl. 1

3. The automatic transmission fluid of claim 2 wherein M is zinc.

4. The automatic transmission fluid of claim 3 wherein X is calcium.

5. The automatic transmission fluid of claim 3 wherein X is barium.

6. The automatic transmission fluid of claim 1 wherein said petroleum naphthenic lubricating oil is obtained by hydrogenating a petroleum naphthenic lubricating oil fraction consisting essentially of about to 25% aromatics, less than about 65% paraflins with the essential balance naphthenes by contact with hydrogen and a sulfur-resistant hydrogenation catalyst at a temperature of about 400 1 wherein to 800 F., and a pressure of about 300 to 5000 p.s.i.g. to provide a hydrogenated oil and hydrogenating said hydrogenated oil by contact with hydrogen in the presence of a platinum group metal hydrogenation catalyst at a temperature of about 400 to 800 F., and a pressure of about 300 to 5000 p.s.i.g., said hydrogenations serving to provide a product having an aromatic content of up to about 31%.

References Cited UNITED STATES PATENTS 2,183,783 12/1939 Bray 208-19 2,289,795 7/1942 McNab 25242.7 2,779,713 1/1957 Cole et al 208-57 2,913,412 11/1959 Moore et a1 25242.7 2,915,452 12/1959 Fear 20857 2,967,146 1/1961 Manley 208-18 3,000,822 9/1961 Higgins et a1.

2,961,408 11/1960 Havely et al. 252 3,039,967 6/1962 Henry et al 252-75 3,070,546 12/1962 PATRICK P. GARVIN, Primary Examiner.

US. Cl. X.R. 25232.7, 42.7, 59, 73

Butler et a1. 252-75 XR 

